A semiconductor optical waveguide having a refraction index varied by a variable electrical field is known from the disclosure of U.S. Pat. No. 4,240,693, issued Dec. 23, 1980, to Johnson, Singh and Uitert, and from the disclosure of U.S. Pat. No. 4,334,774, issued June 15, 1982, to Glass, Kaminow and Olson.
Optical coupling of adjacent waveguides of a semiconductor device is known, for example, as described in U.S. Pat. No. 4,146,297, issued Mar. 27, 1987, to Alferness and Schmidt. Optical waveguides of a semiconductor device can be caused to be proximate each other for a predetermined interaction length separated by a gap. Optical energy transmitted by one of the optical waveguides along the interaction length is coherently coupled into the other waveguide. The waveguides are nonidentical and are fabricated to have respective dispersion (refraction) indices, dispersion characteristics versus wavelength, that are matching or nearly matching at only one wavelength, called the phasematched wavelength. Optical energy with wavelengths the same or nearly the same as the phasematched wavelength will couple from one waveguide to the other waveguide with higher coupling efficiencies than for energy with wavelengths remote from the phasematched value. The indicies can be selected to different values by varying the values of electrical fields established in the waveguides by pairs of electrodes juxtaposed over the two waveguides and along the interaction length. Upon reaching the desired phasematched wavelength, the electrical potentials of the respective pairs of electrodes are perturbed by voltages of equal value and opposite polarity thereby to increase the coupling efficiency.